Stamping and punching processes have long been integral to manufacturing. In a manufacturing plant, there may be hundreds or even thousands of stamping and punching tools. One needs to look no further than the multitude of punched holes in an automobile body to appreciate the importance of punching and stamping operations to modem manufacturing. In a typical punching process, a punch made from a hardened steel alloy is reciprocably located above a body die or platen. A metal sheet/stock or other workpiece is passed below the punch, and the punch is actuated to move downward and pierce a “slug” from the workpiece. Depending on the purpose for punching the workpiece, various hole shapes may be desirable. For instance, where the workpiece is punched for receipt of a conventional fastener, a substantially circular hole may be appropriate. In contrast, other applications such as holes for routing wiring, conduits, or holes for receipt of various plastic mounting members may call for more complex shapes. Different punches are commercially available, having a wide variety of shapes to the working point of the punch, accordingly forming different shaped holes in the workpiece.
The portion of the punching apparatus complementary to the punch comprises the main or lower die. When the punch is moved to a downward position, it is generally desirable to provide a shaped die portion that receives the working point and a portion of the shank of the punch, supporting the punch against lateral deflection and/or breaking as it pierces the workpiece. The prevailing approach in the industry has been to provide a “die button” that is a substantially cylindrical piece press-fit into a bore in the larger, main body die. By forming the die button with a diameter that is very slightly greater than the diameter of the bore, and pressing the button therein, the risk of the button pulling out during operation is minimized. The die button typically includes a central aperture that is shaped substantially complementary to the punch. The aperture has generally been designed to extend all the way through the button, increasing in diameter toward the bottom of the button. Thus, when the punch is lowered into the die button, it pierces a slug from the workpiece, which falls through the button, to be discarded. The press fit interface between the die button and the main body die prevents the punch from withdrawing the button from the body die when retracting.
A related problem involves the challenge of initially placing and subsequently maintaining the die button in the appropriate rotational orientation. If the button aperture is not properly aligned with the punch, excessive wear or breakage of the tools can occur. Die builders often utilize a “dowel” for locating the die button, and preventing its rotation. In a typical design, a longitudinal groove is machined into the side of the button. A complementary groove is also formed in the wall of the bore that receives the button. During assembly, the dowel is inserted into the receiving slot defined by the button and the body die. Because a portion of the dowel is situated in the button and a portion is situated in the wall of the immovable die, the button is properly positioned and prevented from rotation relative to the die.
Over the years, many improvements in punch and die durability and materials have been developed. However, those skilled in the art will appreciate the beating that punch and die tools can take over the course of thousands of hits. Even with the hardest, precision-ground tools, the parts still need relatively frequent sharpening and maintenance, and can and do wear out. Because die buttons are typically press-fit into the main body die for secure retention, a longtime challenge to tool and die shops and die maintenance departments has been the removal of die buttons from the body dies when replacement or sharpening is necessary.
Die builders have taken two general approaches for mounting die buttons in the body dies, and the design style dictates to a large extent the technique used to remove the buttons. In one design, a removable section is machined proximate the die buttons. This removable section or retainer is removed from the main body die, and the buttons are typically removed by inverting the retainer and driving them out with a hammer and metal rod or with an arbor press. In designs wherein the button is not installed in a removable retainer, such as a large die post (which may be a large cast section the size of an automobile), the entire body die must be lifted by an overhead crane, inverted and the buttons forced out of the body die with a hammer, press, etc. In either system, substantial man-hours may be required to replace or sharpen a few die buttons. The punch is not usable during this process, and production is therefore obviously impossible. Various other techniques have been used to remove die buttons, however, most if not all take a considerable amount of time and effort. Moreover, these relatively inelegant techniques risk damage to the die button and the die sections themselves. Overall, maintenance associated with punch die buttons has heretofore been a woefully inefficient endeavor.
The present invention is directed to one or more of the shortcomings or limitations set forth above.